TOEFL Reading: ETS-TOEFL阅读机经 - FZ6UD017UG5G65O4L$

According to paragraph 4, why would removing the Elwha and Glines dams not be enough to restore salmon to the Elwha River? A. They are not the only dams on the Elwha River. B. The lumber and paper mills in Port Angeles also block access to upstream spawning beds. C. Too many species of salmon are competing for survival in one river. D. The dams have left the river's spawning beds in an unusable condition.